The present invention generally relates to cable television system converter boxes, and more particularly relates to converter boxes that receive both NTSC and digital television signals.
Converter boxes, or set top boxes, have long been associated with the reception of cable television programs. In the early years of cable TV, when television sets were capable of receiving only a relatively small number of VHF and UHF channels, converter boxes were needed to receive the large number of channels provided by the cable system and translate them to one of the channels that could be received by the television sets. In most cases, the converter box would demodulate the signal from its original carrier frequency, process the signal, and remodulate it so it could be provided to the television set on channel 2, 3, or 4. Because the converter box outputs the TV signals on a single, selectable channel, such as channel 2, 3, or 4, the user changed channels with the converter box and did not need to change channels on the TV set.
Eventually, television manufacturers produced xe2x80x9ccable-readyxe2x80x9d television sets. These cable-ready TVs could be connected directly to the cable system because their tuners were capable of receiving and demodulating all of the channels provided by the cable TV system. Cable customers with cable-ready TV sets no longer needed cable converters in order to receive basic cable programming.
Subsequent generations of converter boxes have been employed as cable TV companies have continued to offer a variety of new services, such as pay-per-view (PPV) and other premium channels and services. These newer converter boxes were needed to descramble scrambled channels and to provide internet services, program guides, and the like.
Digital television (DTV) refers to television signals that have been encoded and compressed. Currently, High Definition Television (HDTV) is the most common form of digital television signal being contemplated or provided by cable TV companies. In cable TV systems that provide HDTV signals, the HDTV signals are included in the channel lineup along with the NTSC signals. HDTV signals cannot be demodulated by converter boxes with demodulators that are designed for conventional NTSC signals. Therefore, the HDTV signals need to be provided to an HDTV-compatible TV set, or to an HDTV-to-NTSC converter, which converts the HDTV signal to NTSC format and provides the NTSC signal to the NTSC TV set.
In order for the HDTV signals to get to the HDTV-compatible TV set or to the HDTV-to-NTSC converter, the HDTV signals must, in effect, bypass the cable converter. This may be accomplished with a manually controlled switch that is external to the converter box. However, requiring a cable customer to adjust a manual switch whenever an HDTV channel is selected is quite inconvenient for the customer. A more convenient solution is a relay-controlled bypass switch, which automatically bypasses the converter when an HDTV channel is selected.
The problem with either of these bypass solutions is that when they are in the bypass mode, the HDTV signal provided to the HDTV-compatible TV set or the HDTV-to-NTSC converter is at the carrier frequency it was transmitted from the cable headend. This requires the receiver in the TV or HDTV-to-NTSC converter to be tuned to the carrier frequency of the HDTV channel, and then switched back to the selectable channel (e.g., channel 2, 3, or 4) when the customer tunes the converter box to an NTSC channel.
In order to avoid requiring the customer to select different channels on an HDTV-compatible TV set or HDTV-to-NTSC converter, there is a need in the art for a converter box that is capable of automatically passing the DTV signals through the converter and outputting them on the same selectable channel that is used for the NTSC channels.
The present invention satisfies the above-described need by providing a system and method for receiving a cable television signal having a plurality of channels and for providing a selected one of the plurality of channels on an output channel. The cable television signal includes a plurality of channels, which include at least one channel in a first signal format and at least one channel in a second signal format. If the selected channel is in the first signal format, the selected channel is converted to an output frequency corresponding to the output channel and output in the first signal format at the output frequency. If the selected channel is in the second signal format, the selected channel is converted to an intermediate frequency, demodulated, modulated to a frequency corresponding to the output channel, and output on the output channel.